/Engine/Source/Runtime/Slate/Public/Widgets/Text/SlateEditableTextLayout.h
Apply the given style to the currently selected text (or insert a new run at the current cursor position if no text is selected)
void ApplyToSelection ( const [FRunInfo](API\Runtime\Slate\Framework\Text\FRunInfo) & InRunInfo, const [FTextBlockStyle](API\Runtime\SlateCore\Styling\FTextBlockStyle) & InStyle )